For boron neutron capture therapy, a promising cancer therapy under development, knowledge about the subcellular boron distribution is important. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and nonresonant laser secondary neutral mass spectrometry (NR-Laser-SNMS) have been used for examining freeze-fractured, freeze-dried human melanoma cells incubated with sodium mercaptoundecahydro-closo-dodecaborate ((Na2B12H11SH)-B-10,BSH), a B-10 containing drug. With both techniques, elemental and molecular images were obtained from the cancer cells with very high sensitivity and subcellular resolution. The measurement of the K/Na ratio demonstrated that the preparation technique used was appropriate for preserving the chemical and structural integrity of living cells. The boron images showed that the intensity of intracellular and extracellular boron signals was clearly different after incubation of cells in different boron concentrations. (C) 2004 Elsevier B.V. All rights reserved.